Are there other types of dementias besides alzheimer's disease?

Yes. To name the few., alzheimer's dementia; vascular dementia (used to be called multi-infarct dementia); dementia with lewy bodies (dlb). Below is the link with descriptions of various types of dementia and possible etiology: http://www.Alz.Org/dementia/types-of-dementia.Asp.
Yes. Alzheimer's disease or alzheimer's dementia is the most common type of dementia. Roughly 7 out 10 who have dementia have alzheimers. Other common types are are vascular, frontal temporal lobe, lewy body, alcohol or other substance induced types. There are many many rare causes of dementia.

Related Questions

Help please! Is Alzheimer's a type of dementia, or are they two different diseases?

A certain type. Dementia refers to thinking and memory problems that are severe enough to impair a person's ability to do their normal activities. Alzheimer disease is the most common type of dementia. Others are less well known and include vascular dementia (multi-infarct dementia), fronto-temporal dementia, and dementia with lewy bodies. Read more...